1. Field of the Invention
This invention relates to a silica glass crucible, especially a silica glass crucible used in a pulling step for the production of a single crystalline silicon, and particularly provides a structure of avoiding intrusion of foreign matter into an inner face of the manufactured silica glass crucible during storing or conveying of the crucible.
2. Description of the Related Art
In the production of single crystalline silicon, it is common that a silica glass crucible used in the melting of polycrystalline silicon as a starting material is cleaned and inspected after the manufacture, and consequently an acceptable product is packed for delivery. With the increase in the purity of semiconductor materials, it is important to suppress various contaminations during the production of single crystalline silicon, and it is also desired to control contamination of a silica glass crucible to minimum. Concretely, when the silica glass crucible is used for pulling a single crystal, it is taken meticulous care on the contamination by cleaning the inside of the crucible with ultra pure water or the like prior to the use. Therefore, it is first important to prevent the manufactured crucible from contamination even in a period from delivery to use. Especially in recent years, the size of the silica glass crucible tends to be gradually increased for enhancing the production efficiency of single crystalline silicon, and hence it is not easy to handle such a larger-size crucible. For example, such a crucible is apt to be easily contaminated during operation such as inspection or packing after the manufacture.
In order to solve such a problem, it is desired to mechanically pack the silica glass crucible at a cleaned state after the cleaning of the silica glass crucible, and hence an apparatus of automatically wrapping the silica glass crucible at the cleaned state is disclosed in JP-A-2000-219207.
Although it becomes particularly possible to avoid contamination at delivery by wrapping with the apparatus described in the above patent document to store the silica glass crucible at the cleaned state, contamination on the inner face of the crucible is not yet prevented completely.
Onto the outer peripheral face of the silica glass crucible is attached silica starting powder and/or silica pieces (hereinafter referred to as raw material powder) of half-molten state, so that such a raw material powder is easily intruded into the inside of the crucible even after wrapping. The raw material powder may be moved inwardly from a gap between a wrapping sheet and an end face of the crucible and intruded into the inside of the crucible, for example, during conveying of the crucible under a wrapping environment, and further when the wrapping sheet is removed after delivery, the raw material powder remaining on the outer face of an opening portion of the crucible may be still intruded into the inside of the crucible, which could not be avoided. In particular, since the conventional wrapping sheet is a thin vinyl sheet, the raw material powder is generated by rubbing the crucible with the vinyl sheet and thereafter intruded easily into the inner face of the crucible through the gap between the sheet and the end face of the crucible.
Moreover, the crucible may be handled at a state of removing the wrapping sheet, for example, after the delivery to a maker for the production of single crystalline silicon. In this case, there is no means for avoiding the intrusion of foreign matters into the inner face of the crucible. In particular, melting treatment does not necessarily start immediately after polycrystalline silicon as a starting material is charged into the crucible and also the crucible is often stored and held at a state of charging the polycrystalline silicon, during which foreign matters are intruded into the crucible to constitute a factor of obstructing single crystallization in the production of single crystalline silicon.
As mentioned above, there are many opportunities of contaminating the inner face of the silica glass crucible, so that it is desired to provide a way for avoiding such contaminations.